"
If you destroy the mass relays at the end, and the destruction of a mass relay causes an explosion big enough to destroy solar systems (like the one in Arrival). Then doesn't it mean that at the end Shepard essentially destroyed the entire galaxy and killed everyone in it? Shepard is essentially the single biggest mass murderer in the history of the galaxy.

Exactly - that's what I mean by a story rife with plotholes. With such a carefully crafted and detailed universe, plotholes like this should've been detected by even the most cursory glance.

The fact that they didn't speaks volumes. "

Well, it kinda makes sense that the mass relays are destroyed.

Think about it :
Game -> Mass Effect
Reaper Tech -> Mass Relays

Last Mass Effect => End of Mass Relays

I just wished they had gone MGS style, with a two hours talk and video to rap up everything, but in a Serious point of view, nothing good would ever come out of this.

In a response to another post : Being Serious, i never actually believed of the premise : " There are hundreds of bad ass Reapers out there, but we build an unknown weapon, connect it to an unknown thing and will live happilly ever after ".

Being immersed on the game, i already had the sense that the galaxy was fuck*d up. But of course, I would love for Sheppard to be happilly ever after

The ending where Sheppard lives is very weird, everything points to that we was dreaming and then waking up on London. Would love for Bioware to have the Balls to make fake endings ( bad endings ) and didnt tell us about it.